Low voltage surge arrester

ABSTRACT

A secondary surge voltage arrester having a high impact resistant molded housing that is provided with supporting struts for mounting a sparkgap assembly in a desired, predetermined spaced relationship with respect to the interior walls of the housing thereby to minimize the risk of flashover of the sparkgap assembly. The arrester is further characterized by incorporatng a special spring that is effective to maintain a precise sparkgap electrode spacing and at the same time to limit lateral movement of the spark-gap assembly within the housing.

[ Mar. 19, 1974 UnitedStates Patent [191 Reckard et al. I 9

3,258,635 6/1966 Carothers.............................

[ LOW VOLTAGE SURGE ARRESTER.

[75] Inventors: Ronald M. Reckard; Raymond I.

Assistant Examiner-Harvey Fendelman Attorney, Agent, or Firm-Myles P.Vale; Volker R. Ulbrich; Francis X. Doyle [73] Assignee:

[22] Filed:

Appl. No.: 292,079

[57] ABSTRACT A secondary surge voltage arrester having a high impactresistant molded housing that is provided with supporting struts formounting a sparkgap assembly in a desired, predetermined spacedrelationship with re- 92 N 0 WEB 1 3 2 0 @6H /4. 72 1 3 8 M4 m UBW 3y mL h l C C S L U .m 2 1 5 5 spect to the interior walls of the housingthereby to minimize the risk of flashover of the sparkgap assem- 4 3 $73 l 3 e. 00 6D 1 9 66 l. 2 m3 4 n2 ml 3 e S f 0 d l e .I F 8 5 r1 bly.The arrester is further characterized by incorporatng a special springthat is effective to maintain a [56] References Cited UNITED STATESPATENTS precise sparkgap electrode spacing and at the same W m u H" mmne 3 i BGOM 8337 5675 9999 1111 0722 6 60 762 8653 59 oo 2337.

time to limit lateral movement of the spark-gap assembly within thehousing.

12 Claims, 6 Drawing Figures 666 333 555 lll 333 1 LOW VOLTAGE SURGEARRESTER BACKGROUND OF THE INVENTION The invention relates to surgevoltage arresters of a type commonly referred to as lightning arresters.More particularly, it relates to a novel housing and support means for asurge voltage arrester of a type often utilized to protect homeappliances from damage due to lightning strikes or other induced voltagesurges on secondary electric power distribution lines.

In the field of electrical power transmission and distribution, the useof sparkgaps, and combinations of sparkgaps with various types ofnon-linear resistance valves to form lightning arresters, is well known.In general, when a sparkgap is combined with a non-linear resistancevalve to form such an arrester, the spacing of the sparkgap is used todetermine the arrester sparkover protective characteristic while thenon-linear resistance valve is used to reseal the arrester by limitingpower-follow current from the protected power line after a surge voltagehas been discharged to ground through the arrester. Numerous engineeringand design refinements have been made in the structure of sparkgapelectrode arrangements, as well as in the types of materials used tomake non-linear resistance valves for these arresters. However, mostsuch changes have occurred in the area of high voltage arresters, i.e.those used to protect electric distribution or transmission lines ratedto carry power at several thousand volts. On

the other hand, the. designs for secondary surge voltage arresters hastended to remain quite simplified over the years. Specifically, forsurge voltage arresters that are designed to protect equipments fromvoltage surges in the range of 150 to 600 volts, it has become commonpractice to use a simple sparkgap electrically connected in series witha body of pellets or granules of non-linear resistance valve material,which are confined by the inner walls of the arrester housing.

This conventional prior art structure of secondary arresters has beengenerally adequate in the past. However, as the use of electric powercontinues to grow, and particularly as longer secondary voltage powerdistribution lines are used to bring power to remotely located ruralareas, the need for more sophisticated secondary arresters increases. Ofcourse, the greater the length of secondary voltage distribution lines,the higher the associated risk is of either a direct lightning strike oran induced over-voltage surge on the line. Coupled with this heightenedrisk, the steadily larger number of relatively expensive electricalappliances that are being utilized in homes and businesses serves tomultiply the risk of damage due to overvoltage surges on these lines.Thus, there are two major areas in which it is desirable to improvepresent day secondary voltage arresters.

The first of these areas of potential improvement is in the protectivecharacteristics of the arresters. In this regard, it is desirable toassure an accurately controlled sparkover level of such arresters sothat they can be used to provide a precisely known margin of safetyabove the basic insulation levels of the home applidue to moistureleakage around conventional arrester also be caused by formation of alow resistance tracking path along the interior surface of the arresterhousing, adjacent which the arrester components are closely mounted. Asmentioned above, in typical prior art secondary arresters, voltage.limiting valve pellets are simply stacked directly against the interiorwall of the insulating housing of the arrester. This arrangement mayresult in some are tracking of these walls.

The second basic area of desirable design improvements is related to theprime cost of materials and labor needed to construct secondaryarresters. The relatively low sales volume of such arresters, coupledwith the relatively high expenses associated with the sale of one or twoarresters to a given customer, serve to amplify the importance of primecost reductions. At the same time, due to the nature of the applicationof secondary arresters, it is desirable that they be ruggedlyconstructed of high impact resistance materials that will not be easilydamaged during the normal transportation and relatively rough handlingto which the arresters are subjected prior to their installation. Bothas a matter of aesthetic appearance and as a factor of cost reduction,it is desirable to design such arresters as compactly as possible.

SUMMARY OF THE INVENTlON In the preferred embodiment of the inventiondisclosed herein, a secondary voltage arrester is formed of ahigh-impact-resistant plastic material that is molded with integralsupporting struts on its interior surface. The supporting struts arearranged to define supporting planes that are effective to hold asparkgap assembly in spaced-apart relationship with respect to theinterior walls of the arrester. The sparkgap assembly includes a pair ofprecision sparkgaps that are electrically connected in series withblocks of non-linear resistance valve material, to afford two dischargepaths between a pair of line terminals and a ground terminal. A specialspring is used to maintain accurate sparkgap spacing and to also holdthe sparkgap assembly in a spacedapart relationship with respect to theinterior walls of the arrester housing. A plurality of mechanicallydeformable supporting rods are used to cage the sparkgap assembly activecomponents and hold them in a desired operation relationship. Finally,the arrester housing is hermetically sealed with a thermal-setting resinthat encapsulates a plurality of line and ground conductors that areconnected to the terminals of the sparkgap assembly within the arrester,and the final seal is accomplished by ultrasonically welding a cover tothe opposite end of the housing.

A primary object of the invention is to provide a secondary surgevoltage arrester that overcomes the shortcomings of prior art arrestersthat are discussed above.

Another object of the invention is to provide a secondary surge voltagearrester having a molded, high impact resistance insulating housing thatis provided with integral support means for positioning a sparkgapassembly away from the interior walls of the housing.

A further object of the invention is to provide a surge voltage arresterwith a special compression spring that is operable to maintain accuratesparkgap spacing of a sparkgap assembly while at the same time servingto hold the assembly in a predetermined relationship with respect to thearrester housing.

Still another object of the invention is to provide a surge voltagearrester having a sparkgap assembly that is characterized byincorporating a plurality of insulated support rods that form a cagearound the active components of the assembly to hold these components ina predetermined operating relationship.

Still another object of the invention is to provide an hermeticallysealed surge voltage arrester that is very compact in size and thatminimizes the risk of moisture leakage into the arrester housing.

Additional objects and advantages of the invention will become apparentto those skilled in the art from the description of it that is presentedherein, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 2 is an end view, taken along theplane 22 of FIG. 1, showing the interior of the arrester illustrated inFIG. 1, including the operating relationship between an arrester supportmeans and a sparkgap assembly and compression spring that are importantfeatures of the present invention.

FIG. 3 is a side elevation view of the sparkgap assembly illustrated inFIGS. 1 and 2.

FIG. 4 is a perspective view, partly in cross section, of the housing ofthe arrester illustrated in FIGS. 1 and 2.

FIG. 5 is a perspective view of the special compression springillustrated in FIG. 2.

FIG. 6 is a side elevation view of the compression spring illustrated inFIGS. 2 and 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2of the drawing, it will be seen that there is shown a surge voltagearrester 1 comprising a molded insulating housing 2 that has an interiorwall means 3 generally in the form ofa cylindrically walled cup. A highimpact resistant, thermalsetting plastic material is used to form thehousing 2. In this embodiment of the invention the well known,commercially available plastic Lexan, that is sold by General ElectricCompany, through its manufacturing plants in Pittsfield, Mass, is usedto form the molded housing 2. Other equivalent materials may be used inmodifications of the invention. As shown in FIGS. 1 and 2, the arresterhousing 2 includes the cup-shaped portion 2a and a disc-shaped cover 2b.The cover 2b is hermetically sealed to the cup-shaped portion 2a by anultrasonic welding operation. Accordingly, the juncture between thesecomponents is absolutely watertight and the only other possible accessavenue for moisture to the interior of housing 2 is through a passageway4 in the base of the cup-shaped portion 2a.

Mounted within the arrester housing 2 is a sparkgap assembly 5 and aspecial compression spring 6. Integrally molded with the interior wallmeans 3 of the housing 2 is a first set of supporting struts 7 and 7located on one portion (designated by the bracket 8) of the wall means3, to define a first supporting plane (designed by the line 7a). Asecond set of supporting struts 9a, 9b, 9c and 9d is integrally moldedon another portion (designated by the bracket 10) of the wall means 3,to define a second supporting plane (designated by the line numbered9e). It should be understood that the first plane 7a and the secondplane 9e are disposed in substantially parallel relationship to oneanother for purposes of the invention which will become apparenthereinafter. The sparkgap assembly 5 is mounted between the firstsupport plane 711 and the second support plane 9e, in combination withthe compression spring 6, which is mounted between the support plane 92and one terminal of the sparkgap assembly 5.

Before describing the novel features of the sparkgap assembly 5, itshould be understood that various types of precision sparkgap assemblieswill be suitable for practicing the present invention. For example, theprecision sparkgap electrodes disclosed in US. Pat. No. 3,435,290Lyman,which issued Mar. 15, 1969 and is assigned to the assignee of thepresent invention, are suitable for use in practicing this invention.More specifically, the preferred embodiment of the sparkgap assembly 5,as shown in detail in FIGS. 2 and 3, comprises a first sparkgap (notshown) defined between a first electrode 11 and a second, convolutedelectrode 12 which is similar in construction to the sparkgaparrangement of the above-identified Lyman patent. A second sparkgap (notshown) is defined by the first electrode 11 and a third electrode 13. Inorder to limit power follow current across the first and secondsparkgaps of the assembly 5, following the discharge of an overvoltagesurge therethrough, a pair of disc-shaped, non-linear resistance valveblocks 14 and 15 are mounted respectively in electrically conductingrelationship with the second electrode 12 and the third electrode 13 ofthe sparkgaps, and between a pair of flat metal line terminals 16 and17, which are in electrically conducting relationship with the outersurfaces of the valves 14 and 15, as shown in FIG. 3. As explained inthe above-mentioned Lyman patent, the precision spacing of the first andsecond sparkgaps is set by a pair of pressed mica discs 18 and 1.9 thatare mounted between the first electrode, or ground terminal 11 ofsparkgap assembly 5 and the second and third electrodes 12 and 13.Finally, four substantially parallel mounted supporting rods, two ofwhich are designated in FIG. 3 by the identifying numbers 20 and 21 arepositioned through apertures 16' and 17' in both of the line terminals16 and 17 at spaced-apart points around the periphery of the valve discs14 and 15 thereby to form a cage around these valves and the sparkgapelectrodes 11-13. It will be understood that two additional supportingrods are positioned on the opposite side of sparkgap assembly 5. One ofthese supporting rods is shown as the rod 31 in FIG. 2. Pursuant to theinvention, the cage formed by the four support rods (20,21, etc.) iseffective to prevent the electrodes and valves from moving from betweenthe line terminals 16 and 17 even when the arrester 1 is subjected tosevere mechanical shocks.

A novel feature of the invention resides in the construction andinstallation of the support rods 20, 21 and 31. In the preferredembodiment of the invention, these rods are formed of a suitable plasticresin, such as the well-known, commercially available Nylon that is soldby Dupont Corporation through its Wilmington, Del. factory. As best seenin FIG. 3 both ends of all of the support rods 20, 21, (etc.) arecrimped adjacent their respective outer ends to prevent these ends frombeing moved through the apertures 16' and 17 in the line terminals 16and 17. Preferably, this crimping operation is-performed when the rodsare at room temperature, so it is a purely mechanical operation;however, the ends of the rods may be thermally deformed, if desired. Theenlarged portion formed by such crimping is designated in FIG. 3 by thenumerals 21a and 21b on the rod 21 and by the numerals a and 20b on therod 20. The other support rods, such as rod 31 are similarly crimped, asshown at 310 and 31b, in FIG. 1. In addition to serving as a clampingmeans for holding the line terminals 16 and 17 against the valve discs14 and 15, the respective outer ends of the support rods 20, 21, etc.perform an additional function in the present invention. Due to the factthat both ends, e.g. ends 20a20b, 21a- 21b and 31a-31b, etc. extendbeyond the line terminals 16 and 17, they serve as limit stops torestrict the lateral movement of the sparkgap assembly 5 with respect tothe first and second sets of support struts (7-7 and 9a-d). The ends20a, 21a and 31a of support rods 20, 21 and 31, respectively, extendthrough the first support plane 7a past the outer sides of the supportstruts 7 and 7, as best seen in FIG. 2. On the other hand, the lowerends 20b, 21b and 31b of the support rods 20, 21 and 31 are positionedadjacent the outside edges of the compression spring 6 and are limitedin lateral movement by engagement with the spring.

In order to better understand all of the functions of the specialcompression spring 6, reference will now be made to FIGS. 5 and 6 of thedrawing. Preferably, spring 6 is fabricated from bronze plate stock. Asshown, the compression spring 6 in this embodiment of the inventioncomprises a pair of generally flat side members 6a and 6b, which arepositioned in a common plane. A generally flat central member 60 ispositioned between the side members 6a and 6b in another plane. Thecentral member 6c is joined adjacent its ends to the side members 6a and6b adjacent their ends by a pair of resilient connecting arms 6d and 6e,respectively. In order to firmly position the spring 6 against lateralmovement when'it is mounted in its assembled position, as shown in FIG.2, each of the side members 6a and 6b has a pair of integral tabs 60'and 6a" and 6b and 6b projecting out of the common plane in which theside members 6a and 6b lie. As clearly shown in FIG. 2, the projectingtabs 6a and 6b extend past a portion of the second set of struts 9a-9d,toward the wall means 3 of the arrester housing 2. Thus, the tabs 6a and6b, as well as tabs 6a" and 6b", are operable to engage thesepredetermined areas of the second set of struts 9a-9b, thereby toprevent the side members 6a and 6b of spring 6 from being movedlaterally away from the second set of struts 9a and 9b.

Accordingly, because of the constraining operation of tabs 6a, 6a", 6band 6b with respect to the second set of support struts 90-4, and thelimit stop operation of the projecting ends 20a, 21a and 31a of supportrods 20, 21 and 31 on sparkgap assembly 5, as described above, thesparkgap assembly 5 is held in spaced-apart relationship from theinterior wall means 3 of housing 2. This arrangement protects thesparkgap assembly 5 from risk of flashover due to any contamination orarc tracking that might form on the interior wall means 3 of the housing2. A further important function of the compression spring 6 is to biasthe line terminal 17 toward line terminal 16, which is arrested in itsmovement by the first set of support struts 7-7'. This biasing forcemaintains the length of the first and second sparkgaps of sparkgapassembly 5 in their desired predetermined relationship.

In order to more fully explain the novel features of the first andsecond sets of support struts 7--7' and 9a-d, reference will now be madeto FIG. 4 of the drawing. The housing 2 is shown in FIG. 4 as beingbroken away to clearly show the first set of support struts, whichcomprises the pair of struts 7-7. In addition, the second set of supportstruts, comprising the four struts 9a, 9b, 9c and 9d, are clearlyvisible in this figure. It will be noted that each of the struts 9a-d,in the portions thereof, defining the second supporting plane 9e issubstantially as long as the respective side members 6a and 6b of thecompression spring 6 (shown in FIG. 5 Thus, these support struts serveto firmly engage the side members 6a and 6b over a major portion oftheir length. It will be apparent that other support strut arrangementsmay be used in alternative embodiments of the invention; however, it isimportant to provide at least a pair of spaced-apart struts in both thefirt and second sets of supporting struts, in order to assure that thebiasing force applied by compression spring 6 is uniformly distributedaround the peripheries of the first and second sparkgaps of sparkgapassembly 5. Otherwise, the individual sparking points or teeth of thesparkgap assembly 5 (as explained in the abovementioned Lyman patent)may be burned back unevenly to thereby distort the sparkgap spacing.

Now, in order to complete the description of the novel surge voltagearrester of the invention, reference will again be made to FIGS. 1 and 3to describe the preferred means by which the terminals of sparkgapassembly 5 are connected to suitable conductors. As shown in FIG. 3,line terminals 16 and 17 of sparkgap assembly 5 each contain deformabletongue portions 16a and 17a, respectively. These tongue portions arecrimped onto exposed wires 22 and 23', respectively, of a pair ofseparate suitably insulated conductors 22 and 23. In like manner, thefirst electrode or ground terminal 11 of sparkgap assembly 5 contains adeformable tongue portion 11a that is crimped onto an exposed wire 24,part of another insulated conductor 24. Thus, the surge voltage arrester1 may be connected to protect either a one or two-wire powerdistribution system. When a two-wire system is to be protected, the lineconductors 22 and 23 are connected to the respective lines of the powersystem and the conductor 24 is securely connected to a solid electricalground. On the other hand, if a single power line is to be protected,the two sparkgaps of sparkgap assembly 5 can be connected in parallelacross the line by connecting conductors 22 and 23 to the line and byconnecting ground terminal 11, via conductor 24, to a suitableelectrical ground terminal.

In order to provide a water-tight seal around the insulation ofconductors 22-24, as well as around the wires 22'24, they are insertedthrough the passageway 4 in the bottom of the cup-shaped portion 2a ofinsulated housing 2, as shown in FIG. 1. A body of a suitable sealingcompound 25 is positioned in the passageway 4 around the conductors22-24 and, importantly to the present invention, around the inner endsof wires 2224, to thereby hermetically seal thesparkgapassembly-receiving chamber of the housing 2. The reason it isimportant to totally encapsulate the inner uninsulated ends of wires2224' is to prevent moisture from being drawn by capillary action alongthe wires, past the sealant 25. It will be noted (in FIG. 1) that theinner surface 25a of body of compound 25 completely encapsulates each ofthe uninsulated portions of wires 22'24'. The body of sealing material25 may be a conventional epoxy resin or other suitable water-resistantsealing material that has a coefficient of thermal expansionsubstantially identical to the coefficient of thermal expansion of theLexan insulating housing 2, so that the sealant 25 is not cracked orbroken loose from the inner walls of the passageway 4 when the arresterl is placed in service.

From the foregoing description of the invention, it will be apparentthat various modifications and improvements may be made in it withoutdeparting from the true scope and spirit of the invention. Accordingly,it is our intention to define the scope of the invention in thefollowing attached claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A surge voltage arrester comprising a molded insulating housinghaving interior wall means defining a chamber for receiving a sparkgapassembly, a first set of supporting struts mounted on one portion ofsaid wall means to define a first supporting plane, a second set ofsupporting struts mounted on another portion of said wall means todefine a second supporting plane, said first and second supportingplanes being disposed in substantially parallel relationship, a sparkgapassembly mounted between said first and second planes, said sparkgapassembly comprising; first and second spaced-apart electrodes arrangedto form a sparkgap therebetween, an insulating spacer disposed betweensaid electrodes to hold them apart, a non-linear resistance valve, oneside of said valve being positioned in electrically conductingrelationship with said second electrode, and a generally flat metalterminal positioned in electrically conducting relationship with asecond side of said valve, thereby to form a series circuit from saidterminal, through said valve, across said sparkgap to the firstelectrode thereof; in combination with a compression spring mountedunder compression between said first electrode and said second set ofstruts, said spring being effective to bias said first sparkgapelectrode toward said terminal thereby to hold said first and secondelectrodes in spaced-apart relationship against opposite sides of saidspacer, said terminal being positioned in fixed relationship withrespect to said first supporting plane, said spring comprising a pair ofgenerally flat side members positioned in a common plane, a generallyflat central member positioned between said side members in anotherplane, and a pair of resilient connecting arms respectively joining saidside members to said central member, each of said side members having apair of integral tabs projecting out of said common plane, past aportion of said second set of struts, toward the wall means, said tabsbeing operable to engage predetermined areas of said second set ofstruts thereby to prevent the side members of said spring from beingmoved away from said predetermined areas.

2. An invention as defined in claim 1 wherein said connecting arms are,respectively, joined to opposite ends of said central member and tooppositely-disposed ends of said side members.

3. An invention as defined in claim 2 wherein said first and second setsof supporting struts each comprise at least a pair of spaced-apartstruts, each of said struts in the portions thereof defining saidsupporting planes, being substantially as long as the side members ofsaid spring.

4. An invention as defined in claim 2 wherein said spring is formed of asingle piece of bronze plate stock.

5. A surge voltage arrester comprising a molded insulating housinghaving interior wall means defining a chamber for receiving a sparkgapassembly, a first set of supporting struts integrally molded on oneportion of said wall means to define a first supporting plane, a secondset of supporting struts integrally molded on another portion of saidwall means to define a second supporting plane, said first and secondsupporting planes being disposed in substantially parallel relationship,a sparkgap assembly mounted between said first and second planes, saidsparkgap assembly comprising; a plurality of electrodes arranged todefine a first and a second sparkgap, a pair of non-linear resistancevalves, a pair of line terminals, a ground terminal, and a plurality ofsupport rods, said support rods being operable to maintain the lineterminals in spaced apart relationship with the ground terminal disposedtherebetween and with one sparkgap and one valve positioned in seriescircuit relationship, respectively, between each line terminal and theground terminal; in combination with a compression spring mountedbetween one of said line terminals and one of said supporting planesthereby to force the other line terminal against the set of strutsdefining the other supporting plane.

6. An invention as defined in claim 5 wherein said support rods areformed of a deformable plastic resin, each of said support rods beingpositioned through apertures in both of the line terminals thereby toform a cage around said sparkgap electrodes and valves, said cage beingeffective to prevent the electrodes and valves from moving from betweensaid line terminals and the ground terminal.

7. An invention as defined in claim 6 wherein at least one of each ofsaid rods extends beyond one of said line terminals, on opposite sidesof the set of supporting struts adjacent said terminal, thereby to formlimit stops that are operable to engage the sides of said supportingstruts to prevent the sparkgap assembly from being moved laterally awayfrom said struts.

8. An invention as defined in claim 7 wherein said compression springcomprises a pair of generally flat side members positioned in a commonplane, a generally flat central member positioned in another plane, anda pair of resilient connecting arms joining said side members to thecentral member, each of said side members having a pair of integral tabsprojecting out of said common plane, past a portion of said second setof struts, toward the wall means, said tabs being operable to engagepredetermined areas of said second set of struts thereby to prevent saidside members from being moved away from said predetermined areas.

9. An invention as defined in claim 7 wherein each of said rods iscrimped adjacent the respective ends thereof to prevent said ends frombeing moved through the apertures in said line terminals.

10. An invention as defined in claim 9 wherein said plurality ofsupporting rods comprises four substantially parallel-mounted rodsarranged to define the re- 12. An invention as defined in claim 11wherein each of said conductors includes an insulated wire at its innerend disposed in said passageway, and wherein said body of sealingcompound completely encapsulates eachof said uninsulated wires therebyto prevent moisture from being drawn by capillary action along saidwires past the encapsulating compound into thesparkgap-assembly-receiving chamber of said arrester.

1. A surge voltage arrester comprising a molded insulating housinghaving interior wall means defining a chamber for receivIng a sparkgapassembly, a first set of supporting struts mounted on one portion ofsaid wall means to define a first supporting plane, a second set ofsupporting struts mounted on another portion of said wall means todefine a second supporting plane, said first and second supportingplanes being disposed in substantially parallel relationship, a sparkgapassembly mounted between said first and second planes, said sparkgapassembly comprising; first and second spaced-apart electrodes arrangedto form a sparkgap therebetween, an insulating spacer disposed betweensaid electrodes to hold them apart, a non-linear resistance valve, oneside of said valve being positioned in electrically conductingrelationship with said second electrode, and a generally flat metalterminal positioned in electrically conducting relationship with asecond side of said valve, thereby to form a series circuit from saidterminal, through said valve, across said sparkgap to the firstelectrode thereof; in combination with a compression spring mountedunder compression between said first electrode and said second set ofstruts, said spring being effective to bias said first sparkgapelectrode toward said terminal thereby to hold said first and secondelectrodes in spaced-apart relationship against opposite sides of saidspacer, said terminal being positioned in fixed relationship withrespect to said first supporting plane, said spring comprising a pair ofgenerally flat side members positioned in a common plane, a generallyflat central member positioned between said side members in anotherplane, and a pair of resilient connecting arms respectively joining saidside members to said central member, each of said side members having apair of integral tabs projecting out of said common plane, past aportion of said second set of struts, toward the wall means, said tabsbeing operable to engage predetermined areas of said second set ofstruts thereby to prevent the side members of said spring from beingmoved away from said predetermined areas.
 2. An invention as defined inclaim 1 wherein said connecting arms are, respectively, joined toopposite ends of said central member and to oppositely-disposed ends ofsaid side members.
 3. An invention as defined in claim 2 wherein saidfirst and second sets of supporting struts each comprise at least a pairof spaced-apart struts, each of said struts in the portions thereofdefining said supporting planes, being substantially as long as the sidemembers of said spring.
 4. An invention as defined in claim 2 whereinsaid spring is formed of a single piece of bronze plate stock.
 5. Asurge voltage arrester comprising a molded insulating housing havinginterior wall means defining a chamber for receiving a sparkgapassembly, a first set of supporting struts integrally molded on oneportion of said wall means to define a first supporting plane, a secondset of supporting struts integrally molded on another portion of saidwall means to define a second supporting plane, said first and secondsupporting planes being disposed in substantially parallel relationship,a sparkgap assembly mounted between said first and second planes, saidsparkgap assembly comprising; a plurality of electrodes arranged todefine a first and a second sparkgap, a pair of non-linear resistancevalves, a pair of line terminals, a ground terminal, and a plurality ofsupport rods, said support rods being operable to maintain the lineterminals in spaced apart relationship with the ground terminal disposedtherebetween and with one sparkgap and one valve positioned in seriescircuit relationship, respectively, between each line terminal and theground terminal; in combination with a compression spring mountedbetween one of said line terminals and one of said supporting planesthereby to force the other line terminal against the set of strutsdefining the other supporting plane.
 6. An invention as defined in claim5 wherein said support rods are formed of a deformable plastic resin,each of said support rods being positioned through apertures in both ofthe line terminals thereby to form a cage around said sparkgapelectrodes and valves, said cage being effective to prevent theelectrodes and valves from moving from between said line terminals andthe ground terminal.
 7. An invention as defined in claim 6 wherein atleast one of each of said rods extends beyond one of said lineterminals, on opposite sides of the set of supporting struts adjacentsaid terminal, thereby to form limit stops that are operable to engagethe sides of said supporting struts to prevent the sparkgap assemblyfrom being moved laterally away from said struts.
 8. An invention asdefined in claim 7 wherein said compression spring comprises a pair ofgenerally flat side members positioned in a common plane, a generallyflat central member positioned in another plane, and a pair of resilientconnecting arms joining said side members to the central member, each ofsaid side members having a pair of integral tabs projecting out of saidcommon plane, past a portion of said second set of struts, toward thewall means, said tabs being operable to engage predetermined areas ofsaid second set of struts thereby to prevent said side members frombeing moved away from said predetermined areas.
 9. An invention asdefined in claim 7 wherein each of said rods is crimped adjacent therespective ends thereof to prevent said ends from being moved throughthe apertures in said line terminals.
 10. An invention as defined inclaim 9 wherein said plurality of supporting rods comprises foursubstantially parallel-mounted rods arranged to define the respectivecorners of a square within which said sparkgap assembly is caged.
 11. Aninvention as defined in claim 5 including; means defining a passagewaythrough the wall means of said housing, three insulated conductorsextending into said passageway, said conductors being electricallyconnected, respectively, to said line terminals and the ground terminal,and a body of sealing compound positioned in said passageway around saidconductors to hermetically seal said chamber.
 12. An invention asdefined in claim 11 wherein each of said conductors includes aninsulated wire at its inner end disposed in said passageway, and whereinsaid body of sealing compound completely encapsulates each of saiduninsulated wires thereby to prevent moisture from being drawn bycapillary action along said wires past the encapsulating compound intothe sparkgap-assembly-receiving chamber of said arrester.